During the last decades, in parallel with the evolution of social and cultural environment, modern psychiatry has faced the emergence of new psychopathological conditions, characterized by peculiar clinical pictures. This is the case of orthorexia nervosa (ON), a condition described for the first time by Steve Bratman in the late 1990s . ON features an eating pattern mainly characterized for an abnormal fixation and obsession for a healthy style of eating (Bratman, 1997). The word "orthorexia" derives from the Greek “ortho”, which means “correct / adequate”, and “orexis”, which means “appetite”. Individuals affected by this condition usually adopt restrictive dietary habits, progressively excluding more and more foods considered unhealthy from their diet. Despite the persistence of diagnostic uncertainty for this condition, which to date is not included in the fifth edition of the Diagnostic and Statistical Manual of Mental disorders (DSM-5) , a wide range of possible risk factors has been proposed, such as an individual or family history of other mental disorders, previous overweight or obesity, neurotic or perfectionist personality traits. or also the presence of a high income. Other features associated with ON were the previous presence of specific dietary habits, such as veganism or vegetarianism, a high income or a high intermediate level of instruction. In addition, specific populations, such as athletes or health workers, seem to show a greater risk towards the development of ON symptoms . According to previous studies, the prevalence of ON may vary depending on the kind of sample considered, ranging from 1–57.6% in the general population  and from 35–57.8% in high-risk groups. The distribution of ON in the two sexes is still debated. Several studies reported a higher prevalence among females, although with a lower male/female ratio with respect to AN . However, not all the studies confirmed this result . To date, several instruments were developed for measuring ON. The most frequently employed questionnaire in this field is the ORTO-15 , although this instrument has been increasingly criticized due to the lack of reliability and adherence to the ON symptoms. In particular, the ORTO-15 was developed and validated several years ago, before a more shared agreement on ON definition and features was reached in the scientific literature . Only recently Rogoza and Donnini  proposed a revised version of the instrument, the ORTO-R, which was developed to be in line with the more updated descriptions of ON and reported promising results in the validation study.
Some authors suggested that the spreading of ON may mirror the spreading of the contemporary ideal of healthy eating, which is gradually replacing the ideal of thinness typical of the 1980s and 1990s: in this framework, ON might be considered a restrictive eating disorder in the same psychopathological spectrum of restrictive Anorexia nervosa (AN-R), with different presentations linked to environmental factors . Several studies, in line with this hypothesis, highlighted the similarities between AN and ON, stressing that, despite the shift of the focus on food quality rather than food quantity, these conditions would share a common symptomatology core and would also be associated with similar personality traits, such as perfectionism or inflexibility . On the other hand, ON has been also associated with other psychopathological dimensions, such as the obsessive-compulsive spectrum, stressing the presence of rituals, repetitive behaviours and perfectionism traits in both the disorders . At the same time, increasing literature reported the presence of a possible association between AN and female phenotypes of Autism Spectrum Disorder (ASD). ASD is a neurodevelopmental disorder characterized by an impairment in social communication and interactions, narrow interests and repetitive behaviours, which shows a dramatically higher prevalence among males (while AN shows instead a great prevalence among females) . Since the '70s, some authors reported a familial aggregation between AN and ASD as well as similar clinical features . It was pointed out that the strict focus on food and diet and the ritualized behaviours linked to food intake typical of AN may resemble the pattern of narrow interests and repetitive behaviours of ASD more than the obsessions and compulsion of obsessive-compulsive disorder . In addition to a pattern of rigid habits, inflexibility and narrow interests, the presence of deficits in socio-emotional reciprocity and alterations in theory of mind was also reported among AN patients, further stressing its symptomatological overlaps with the autism spectrum . Several studies in the last years reported, among patients with AN, a higher prevalence of ASD . The presence of subthreshold autistic traits (AT) was reported to be particularly higher among subjects with AN , although increased AT were also found in patients with Bulimia nervosa and Binge eating disorder, which were often been associated with mood disorder spectrum in the literature .
It should be noted that the label of “AT” is used for describing the presence of symptoms and traits similar, although sub-threshold, to those reported by subjects with ASD. In line with the spectrum model, which features a dimensional approach to psychopathology and recognizes the presence of a continuum between full-blown disorders and isolated, atypical or more nuanced symptoms , AT seems to be distributed in a continuum from the general to the clinical population, being particularly represented in some specific high risk groups, including subjects with other kinds of psychiatric disorders . The similarities between AN and autism spectrum, together with the inverse prevalence of these conditions in the two sexes, led some authors to hypothesize that AN might be re-conceptualized as a female-specific phenotype of ASD . The possible link between autism spectrum and AN was further supported by studies focused on female presentations of ASD, which reported that autistic-like symptoms may be underrecognized among females due to the presence of different features with respect to those typical of males. In particular, ASD females seem to report a lower impairment in social relationships, showing a higher ability to cope with the social environment through camouflaging strategies, although reporting more often social anxiety symptoms. Moreover, female forms of ASD would feature different kinds of restricted interests, such as spending time with animals, focusing on fictions or celebrities, or also on food and diet . Despite this amount of studies about the link between autism spectrum and AN, limited research focused on evaluating the possible association between ON and AT. However, as in the case of AN, the obsession with a healthy diet, the ritualized behaviours associated with the preparation and consumption of food, with a selective and narrow interest towards diet, seems to show several overlaps with autistic-like symptomatology. Similarly, the sense of moral superiority and the intolerance towards the eating habits of other people may recall the deficits of the socio-emotional reciprocity typically found in autistic patients . A previous study by Carpita et al.  showed, in a wide University population (students as well as University workers), a greater presence of AT among subjects with ON symptoms, measured by means of the ORTO-15. Moreover, they found that being females and reporting higher AT were statistically predictive factors towards the presence of ON. While this study seems to further support the hypothesis that ON may be associated, like AN, with female presentations of the autism spectrum, the use of ORTO-15, as reported above, was criticized by previous studies.
In this framework, the aim of the present study was to investigate the presence of ON symptoms, measured by means of the ORTO-R, in a sample of University students with or without AT, specifically focusing on evaluating the role of sex and of dietary habits in the association between ON and autism spectrum.